In recent years, a nitride semiconductor luminescent element having an emission layer composed of a III-V group nitride semiconductor or the like has been a focus of attention. In one example, the structure of this luminescent element is composed in the manner that a sapphire substrate is used and there are formed, respectively, an emission layer made of InGaN or the like, a contact layer made of an n+-GaN layer doped with silicon (Si) on the lower portion of the emission layer, an electron blocking layer made of p-AlxGa1-xN doped with magnesium (Mg) on the upper portion of the emission layer, and a contact layer made of p-GaN on the upper portion of the electron blocking layer.
At present, such a GaN device as described above is formed on a substrate of c-plane growth. In order to further enhance the performance of an LED, an LD and the like, however m-plane growth is promising as an alternative to c-plane growth. In the case of an m-plane, an m-plane “p” layer having electrical conductance 20 times as high as that of a c-plane “p” layer has been reported. This “p” layer greatly contributes to the improvement of electrical characteristics, including the enhancement of current diffusion and the lowering of forward voltage. In addition, the m-plane has a crystal polarity perpendicular to a crystal growth surface and is, therefore, a nonpolar plane capable of negating high electric fields inherent in a crystal. Consequently, by performing crystal growth using the nonpolar m-plane, it is possible to increase an overlap of wave functions between electrons and holes and thereby obtain various advantages. Examples of these advantages include the realization of more enhanced internal quantum efficiency (whereby radiative recombination efficiency can be increased) and the realization of higher injection efficiency. Until now, however, an extremely expensive SiC or LiAlO2 substrate, for example, has been necessary for the luminescence of GaN in the m-plane.
Hence, Japanese Patent Laid-Open No. 2006-124268 discloses performing the crystal growth of ZnO in the m-plane by using a solvothermal method and adjusting an angle formed between a seed crystal and the convection direction of a solvent.
In the above-described related art, a seed crystal, such as ZnO, is grown using a liquid phase method (solvothermal method). Accordingly, in order to fabricate a device, the substrate in process needs to temporarily taken out of a furnace and once again processed into a device using an MOCVD method or the like. Thus, the process of the related art is cumbersome and complicated, compared with a vapor phase method in which a process from the fabrication of a substrate to the fabrication of a device can be carried out continuously.
In addition, the Japanese Journal of Applied Physics, 45, L154 (2006) describes a method, in which an m-plane sapphire substrate is used, as a method for growing nonpolar GaN. In that method, however, m-plane GaN does not grow and only semipolar GaN is obtained.